1. Field of the Invention
This invention relates in general to mobile phone networks, and more specifically, to push-to-talk-over-cellular (PoC).
2. Description of Related Art
Advanced voice services (AVS), also known as Advanced Group Services (AGS), such as two-way half-duplex voice calls within a group, also known as Push-to-Talk-over-Cellular (PoC), Push-to-Talk (PTT), or Press-to-Talk (P2T), as well as other AVS functions, such as Push-to-Conference (P2C) or Instant Conferencing, Push-to-Message (P2M), etc., are described in the co-pending and commonly-assigned patent applications cross-referenced above and incorporated by reference herein. These AVS functions have enormous revenue earnings potential for wireless communications systems, such as cellular networks and personal communications systems (PCS) networks.
Currently, there are two major approaches employed in providing advanced voice services in wireless communications systems. One approach is based on circuit-switched technology, wherein voice circuits are reserved during the entire duration of an AVS or PoC call. Circuit-switched PoC is deployed by many operators around the world with technologies such as NEXTEL's iDEN and Kodiak Network's RTX.
Another approach to PoC is based on packet or voice-over-IP (VoIP) technologies. This approach capitalizes on the “bursty” nature of PoC conversations and makes network resources available only during talk bursts and hence is highly efficient from the point of view of network and spectral resources. This approach promises compliance with newer and emerging packet-based standards, such as GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunications System), 3G, 4G, LTE, etc.
Nonetheless, there is a need in the art for improvements to the methods and systems for delivering the advanced voice services, such as PoC, that comply with both existing and emerging wireless packet-based standards and yet provide superior user experiences. Many existing implementations of PoC suffer from an inferior user experience, such as slow call setup. The present invention satisfies the need for a superior user experience, and also defines procedures for practical implementation of PoC in commercial, standards-based, cellular networks, with a focus on features, such as provisioning, fault tolerance, roaming support, support for SIM swap and dual SIM, interaction of PoC with GSM cellular calls, etc.